Textile fibre reinforced absorbent material

ABSTRACT

An absorbent material comprising a mat of dry-formed cellulose fibers integrated with an air-laid non-woven gauze of reinforcing textile fibers. A method of producing this material by air-laying textile fibers on a wire to form a non-woven gauze, whereafter a mat of cellulose fibers is formed on the textile fiber non-woven gauze. The use of the material as an absorbent structure in an absorbent product. A method of producing an absorbent structure comprised of cellulose fibers and reinforcing textile fibers in which a mat of dry-formed cellulose fibers integrated with an air-laid non-woven gauze of reinforcing fibers is defined and mat-formed. An absorbent structure obtained by this method.

[0001] The present invention relates to an absorbent material that has improved mechanical strength and that includes a mat of dry-formed cellulose fibers. The invention also relates to a method of producing such a material and to its use.

[0002] The inventive material is intended for use as an absorbent structure in an absorbent article, such as a sanitary napkin, tampon, panty liner, incontinence guard, diaper, bed protector, bandage, saliva absorbent and the like. The material may either be used immediately without defibering the material or subsequent to defibering the material and forming a mat for an absorbent core.

[0003] It is known from International Patent Application WO 90/05808 to fabricate a pulp web for later defiberation with the aid of a dry forming process, so-called dry-formed reel pulp. A controlled flow of flash-dried paper pulp fibers, which may be a thermomechanical pulp, chemithermomechanical pulp, CTMP, or chemical paper pulp, sulphite or sulphate pulp, having a dry solids content of about 80% is delivered with the aid of an air flow to a forming head mounted above a wire and there formed into a web having a weight per unit area of 300-1500 g/m² and a density of 550-1000 kg/m³. The air is removed by suction through a suction box disposed beneath the wire. The process moisture content shall be 5-30%.

[0004] The web is pre-pressed so as to slightly reduce the bulk of the web prior to finally pressing the web to a density of 550-1000 kg/m³. The pressed web is sufficiently strong to enable it to be rolled-up or handled in sheet form for storage and transportation purposes. It can readily be defibered and is intended to be transferred in a fluffed state for use in the manufacture of absorbent bodies in diapers, sanitary napkins and like products.

[0005] One of the advantages afforded by this material is that the pulp obtains a low hydrogen bond concentration, and consequently the amount of energy required to defiber the pulp is less than that required to defiber a conventional wet-formed pulp. The lower number of hydrogen bonds also enables the material to be heavily compressed while retaining the low defibering energy input requirement. Superabsorbents may also be admixed with the dry-formed material during its manufacture, which is not possible in the manufacture of a wet-formed material.

[0006] It is also known from International Patent Application WO 94/10956 that such a material can be used directly as an absorbent structure, without defibering and fluff-forming the material. In this regard, the absorbent structure includes a dry-formed sheet containing cellulose fibers and having a density of between 0.2 and 1 g/cm³ and a weight per unit area of between 30 and 2000 g/m². This material has very good dispersion properties and swells markedly when wetted. When the material is softened, soft absorbent cores can also be obtained while retaining the good dispersion properties.

[0007] One drawback with the aforedescribed dry-formed materials is their mechanical weakness, both in a non-defibered state and in a defibered and mat-formed state.

[0008] To overcome this problem WO 94/10956 suggests increasing the network strength by reinforcing the structure of the dry-formed roll pulp by adding reinforcing fibers, binding fibers or binding agent to the cellulose fiber mixture. It should also be possible to incorporate a reinforcing layer of plastic, non-woven, net or threads in the absorbent structure or fastening a reinforcing layer on one or both sides of the material.

[0009] When adding reinforcing fibers to flash-dried pulp fibers during dry-laying or to cellulose fibers obtained by defiberation of wet-formed roll or sheet pulp it is necessary to use short and rigid reinforcing fibers. Long and soft fibers will tangle together when included in the air flow of cellulose fibers.

[0010] When using a reinforcing layer it is necessary to make the cellulose fiber layer and reinforcing layer adhere to each other, for instance by adding an adhesive. However, the adhesive will make the end product more rigid and also limit the absorbancy.

[0011] U.S. Pat. No. 3,984,898 describes a method and an apparatus for producing multilayer fibrous mats comprising alternate short and long fiber layers. The apparatus comprises a long fiber defiberating unit feeding long fibers to a chute means directing the fibers to a wire. A short fiber defiberating unit shreds and defiberates woodpulp, disperses the obtained fibers and deposits them on the long fiber mat. The intention is to achieve interfiber bonds at the interface between the layers. However, the mats formed will only have weak bonds easily broken and delamination will easily occur. Therefore, spraying of the very thin long fiber layer or layers with binder is recommended. Further, the long fiber web is deposited by the lickerin method which gives a low productivity. It is only possible to obtain a weight per unit area of about 3 g/m². It may therefore be necessary to use more than one lickerin unit.

[0012] The object of the present invention is to provide a dry-formed material that is suited both for defiberation and mat-forming and for direct use as an absorbent material, optionally after softening the material.

[0013] This object is achieved with an absorbent material that comprises a mat of dry-formed cellulose fibers and is characterized in that the mat is integrated with an air-laid nonwoven gauze layer of reinforcing textile fibers. The nonwoven layer and the cellulose fiber mat may be integrated with one another to an extent in which a homogenous or essentially homogenous material is obtained. The inventive absorbent material may also be a clearly defined multi-layer material in which the boundary layers are integrated with one another. When one layer is thin in relation to the other, the thinner layer may be fully integrated in the thicker layer, which then includes an essentially homogenous distribution of the fibers from the other layer within a zone.

[0014] The inventive material may conveniently have a density of 0.1-1 g/cm³, particularly 0.2-0.9 g/cm³, preferably 0.3-0.8 g/cm³ and most preferably 0.4-0.7 g/cm³. The weight per unit area may be 30-2000 g/m², suitably 50-1500 g/m², particularly 100-1000 g/m² and preferably 200-800 g/m².

[0015] According to the invention, the material may be produced by air-laying textile fibers on a wire to form a non-woven gauze, whereafter mat-forming of the cellulose fibers is effected on the textile fiber non-woven gauze, e.g. with the aid of an air-laying apparatus. The cellulose fibers will penetrate into the non-woven gauze and be integrated therewith.

[0016] To obtain the integration of the short fiber cellulose layer and the longer fiber textile layer this second layer must be a non-woven gauze enabling the cellulose fibers to effectively penetrate the fiber interstices and thus form an integrated layer with the textile fibers.

[0017] Formation of the non-woven gauze layer requires the use of a card, for instance a Fehrer K21 card. The simple laying down of long fibers on a wire described in U.S. Pat. No 3,984,898 will not produce a porous, easily penetrated gauze. Therefore, the layers in the product obtained according to U.S. Pat. No. 3,984,898 requires spraying with a bonding agent to achieve a sufficient degree of interbonding. On the contrary, the present reinforced product is an integrated article not requiring any bonding agent.

[0018] Textile fibers are very likely to tangle together. When cellulose fibers and textile fibers are delivered to a wire simultaneously, the latter fibers will not be uniformly distributed unless they are sufficiently short and rigid. The present invention overcomes this problem.

[0019] The reinforcing fibers will conveniently have a length of 10-100 mm, particularly 32-60 mm. Fibers of this length cannot be used in the reinforcement of wet-formed pulp.

[0020] One advantage of using textile fiber reinforcement in the dry-formed material is that the low hydrogen bond concentration of the material enables it to be defibered in a gentler fashion than wet-formed pulp, without damage to the fibers. The reinforcing effect is thus retained when defibering the material and in the subsequent mat-forming process. The long textile fibers provide a better reinforcement and are also cheaper than the short reinforcing fibers used in wet-formed pulp.

[0021] The textile fibers will conveniently have a gauge or linear density of 1-30 dtex, preferably 1-20 dtex. When reinforcing pulp that is to be defibered, the textile fibers will have a preferred gauge of 1-5 dtex.

[0022] When the material is intended to be defibered for forming an absorbent core, the material will conveniently contain 1-10%, particularly 2-8%, preferably 3-6% reinforcing fibers calculated on the weight of the material in a dry state.

[0023] When the material is intended for direct use, without intermediate defiberation, the reinforcing layer may similarly correspond to 1-10%, particularly 2-8%, preferably 3-6% reinforcing fibers, calculated on the weight of the material in a dry state. The layer will then function essentially as a reinforcement. However, this layer can also impart to the two-layer material a soft surface that may also have a suitable color, particularly may be whiter than the cellulose layer. It is also possible in this case to use a much thicker layer and therewith produce a two-layer material in which the textile fiber layer, for instance, functions as an acquisition layer and the cellulose layer as a storage layer. In this case, the cellulose layer may include superabsorbents and be made relatively thin. The weight ratio between the layers may then be from 20:80 to 80:20, particularly from 35:75 to 75:35.

[0024] When the textile fiber layer is to function as an acquisition layer, the textile fibers will preferably be relatively coarse, e.g. have a gauge of 5-30 dtex, particularly 10-25 dtex and preferably 15-20 dtex.

[0025] The weight per unit area of the textile fiber layer is suitably at least 5 g/m², especially at least 8 g/m² and preferably about 10-20 g/m², when this layer is intended as a reinforcing layer. When the non-woven gauze layer is to be used as an acquisition layer, the weight per unit area may be higher, for instance 20-1200 g/m², especially 40-800 g/m² and preferably 60-700 g/m².

[0026] The invention will now be described with reference to the accompanying drawing, which illustrates schematically an inventive method for the manufacture of the inventive absorbent material.

[0027] The inventive absorbent material is produced by air-laying textile fibers on a wire 5 to form a non-woven gauze 6 with an air-doffing apparatus 1, e.g. with the aid of a Fehrer K21 card. The non-woven gauze, which becomes anchored to the wire in the air-laying process, then passes at least one cellulose pulp air-laying apparatus, such as a Kröyer is head 2 or the like, whereby a mat of flash-dried cellulose fibers is formed on the textile fiber non-woven gauze. Suction boxes 8 are disposed beneath the wire 5 opposite the card 1 and the Kröyer head or Kröyer heads 2. The two-layer material is removed from the wire 5 and passes through a calendar 3, whereafter the material is rolled-up as finished material 4.

[0028] The finished material 4 can be used directly as an absorbent structure with no intermediate defiberation and optionally after being softened. The dry-laid cellulose material retains its effective absorptive and dispersive properties. The mechanical strength of the material is greatly improved by the textile fiber non-woven gauze. Because the non-woven gauze is orientated towards one surface of the absorbent material, it can also be used to provide colored material on one side of the absorbent material for instance, or to form a two-layer material whose layers have mutually different properties. This may be achieved by using different types of reinforcing fibers that have different suction properties and different thicknesses for instance. This enables the suction properties of the material to be influenced.

[0029] It is also possible to “layer” different absorption properties in a structure, by using a sufficiently large amount of textile fibers that possess other suction characteristics than the pulp and then folding the material double or laying the material in several layers.

[0030] Because the dry-formed pulp has low binding energy, the material is easy to defiber and to form a mat reinforced with textile fibers. The textile fibers retain their length and other properties to a substantial extent. This results in an homogenous, reinforced, absorbent structure.

EXAMPLE 1

[0031] Wet-formed HTCTMP with an admixture of about 3% rayon fibers, 12 mm, 1.7 dtex was produced by way of reference. The material was defibered and mat-formed. A network strength of 5.5 N was obtained. A network strength of 3-4 N was obtained with pure HTCTMP.

[0032] Samples according to the invention were then prepared. The results are set forth in the following Table 1. TABLE 1 Sample Admixture of 1.7 dtex viscose Network strength No. % Fibre length N Ref. about 3 12 5.5 1 2.3 40 5.3 2 5.3 40 4.8 3 3.0 50% 12.50% 40 5.0 4 5.3 ″ 6.0 5 5.3 ″ 6.1 Pure 0   3-4 CTMP

[0033] A network strength that equalled the network strength of the reference material was obtained already with an admixture of 2.3% 40 mm fibers. An admixture of 5.3% of a mixture of 50% 12 mm and 50% 40 mm viscose fibers gave a network strength of about 6%. Samples 4 and 5 were comprised of the same material where defiberation treatment was carried out from the cellulose side in the first case and from the viscose fiber side in the second case. Essentially, the same results were obtained.

EXAMPLE 2

[0034] Pure dry-formed HTCTMP and HTCTMP dry-formed on a polyester non-woven gauze “Grilene” comprised of fibers of 38 mm, 1.7 dtex, were produced. The density, weight per unit area, maximum shear force, elongation at maximum shear force and ultimate elongation were measured, the last-mentioned properties before and after ageing treatment under 50 cycles. In respect of the textile fiber reinforced material, these magnitudes were determined without softening the sample (a) and after softening the sample (b), respectively. Residual shear force was calculated as the ratio between the maximum shear forces subsequent and prior to ageing respectively. As evident from the following Table, this value increased from 33% in the case of pure HTCTMP to 95-125% in respect of the inventive material. Other magnitudes, particularly stretchability, were also greatly improved after fiber reinforcement. TABLE 2 Pure 6 7 8 9 Sample CTMP a b a b a b a b Fibre content 0 9.7 6.9 5.6 4.2 Density before compression, kg/m³ 360 Density after compression, kg/m³ 420 467 350 657 356 734 390 776 383 Weight per unit area before 440 compression, g/m² Weight per unit area after 450 440 421 456 426 459 418 440 435 compression, g/m² Max. shear force, N I 1.4 3.3 2.4 2.8 2.1 2.4 1.7 2.3 1.7 II 0.5 3.5 3.0 2.9 2.1 2.3 1.5 2.2 1.6 Elongation at max. I 31 145 116 90 84 52 44 50 41 shear force, % II 32 158 168 159 158 47 132 80 104 Ultimate elongation, % I 67 294 301 280 267 287 291 275 279 II 113 293 319 267 294 284 304 311 279 Residual shear force, % 33 107 125 104 101 99 87 96 95 

1. An absorbent material comprising a mat of dry-laid cellulose fibers integrated with an air-laid non-woven gauze comprised of reinforcing textile fibers obtained by directly dry-laying the cellulose fibers on the newly formed gauze of textile fibers so that the cellulose fibers achieve a sufficient bonding with the textile fibers without any bonding agent.
 2. An absorbent material according to claim 1 , wherein the reinforcing textile fibers have a length of 10-100 mm.
 3. An absorbent material according to claim 1 , wherein the reinforcing textile fibers have a length of 32-60mm.
 4. An absorbent material according to claim 1 , which includes up to 10% by weight reinforcing fibers, calculated on a total weight of the absorbent material.
 5. An absorbent material according to claim 4 , which contains 2-8 % reinforcing fibers.
 6. An absorbent material according to claim 4 , which contains 3-6 % reinforcing fibers.
 7. An absorbent material according to claim 1 , wherein the reinforcing fibers are natural fibers or synthetic fibers.
 8. An absorbent material according to claim 7 , wherein the reinforcing fibers are cotton fibers, rayon fibers or polyester fibers.
 9. An absorbent material according to claim 1 , wherein the weight ratio between the cellulose fiber layer and the textile fiber layer is from 20:80 to 80:20.
 10. An absorbent material according to claim 9 , wherein the weight ratio is from 35:75 to 75:35.
 11. An absorbent material according to claim 9 , wherein the textile fibers have a gauge of 5-30 dtex.
 12. An absorbent material according to claim 11 , wherein the gauge is 10-25 dtex.
 13. An absorbent material according to claim 11 , wherein the gauge is 15-20 dtex.
 14. An absorbent material according to claim 4 , wherein the textile fibers have a gauge of 1-10 dtex.
 15. An absorbent material according to claim 14 , wherein the gauge is 1-4 dtex.
 16. A method of producing an absorbent material that includes a mat of dry-laid cellulose fibers integrated with an air-laid non-woven gauze comprised of reinforcing textile fibers, comprising: air-forming textile fibers with an air-doffing apparatus on a wire to form a non-woven gauze; and directly dry-laying the cellulose fibers on the newly formed non-woven gauze of textile fibers to integrate the cellulose fibers with the non-woven gauze and form a mat wherein the cellulose fibers achieve a sufficient bonding with the textile fibers without any bonding agent.
 17. A method according to claim 16 , wherein the reinforcing textile fibers have a length of 10-100 mm.
 18. A method according to claim 17 , wherein the length is 20-80 mm.
 19. A method according to claim 17 , wherein the length is 32-60 mm.
 20. A method according to claim 16 , wherein the material contains up to 10% by weight reinforcing fibers, calculated on a total weight of the absorbent material.
 21. A method according to claim 20 , wherein the material contains 3-8% reinforcing fibers.
 22. A method according to claim 16 , wherein the reinforcing fibers are natural fibers or synthetic fibers.
 23. A method according to claim 22 , wherein the reinforcing fibers are cotton fibers, rayon fibers or polyester fibers.
 24. A method according to claim 16 , wherein the weight ratio between the cellulose fiber layer and the textile fiber layer is from 20:80 to 80:20.
 25. A method according to claim 24 , wherein the weight ratio is from 35:75 to 75:35.
 26. A process for producing an absorbent product, comprising: air-forming textile fibers with an air-doffing apparatus on a wire to form a non-woven gauze; directly dry-laying the cellulose fibers on the newly formed non-woven gauze of textile fibers to integrate the cellulose fibers with the non-woven gauze and form a mat wherein the cellulose fibers achieve a sufficient bonding with the textile fibers without any bonding agent; and including the mat in an absorbent product.
 27. A process according to claim 26 , wherein the integrated mat of cellulose fibers and non-woven gauze is directly incorporated in an absorbent product without intermediate defiberation.
 28. A process according to claim 26 , wherein the integrated mat of cellulose fibers and non-woven gauze is defibered and mat-formed into an absorbent core that is then incorporated into an absorbent product.
 29. An absorbent structure including cellulose fibers reinforced with textile fibers, the structure having been produced by defiberating and mat-forming an absorbent material comprising a dry-laid mat of cellulose fibers integrated with an air-laid non-woven gauze of long reinforcing textile fibers, wherein the absorbent material is obtained by directly dry-laying the cellulose fibers on the newly formed gauze of textile fibers so that the cellulose fibers achieve a sufficient bonding with the textile fibers without any bonding agent.
 30. A method of producing an absorbent structure including cellulose fibers and reinforcing textile fibers, comprising: air-forming textile fibers with an air-doffing apparatus on a wire to form a non-woven gauze; directly dry-laying the cellulose fibers on the newly formed non-woven gauze of textile fibers to integrate the cellulose fibers with the non-woven gauze and form a mat wherein the cellulose fibers achieve a sufficient bonding with the textile fibers without any bonding agent; and defiberating and mat-forming the integrated mat of cellulose fibers and non-woven gauze.
 31. An absorbent material according to claim 1 , wherein the reinforcing textile fibers have a length of 20-80 mm.
 32. A process according to claim 26 , wherein the absorbent product is one of a diaper, sanitary napkin, tampon, panty protector, incontinence guard, bed protector, wound or sore dressing, and a saliva absorbent. 